Stimulation induced analgesia has been in clinical use for more than ten years and thousands of patients have been treated. There is no unifying theory to explain the effects of the various forms of stimulation. One possibility is that electrical stimulation of the nervous system activates local or central pathways which utilize naturally occurring opiates to suppress pain. If this is the case, then the administration of an opiate antagonist (Naloxone) should reverse stimulation induced analgesia. In the patient population of the Pain Treatment Center of the Johns Hopkins Medical Institutions, there are a significant number of patients achieving satisfactory pain relief with transcutaneous peripheral nerve, spinal cord, and brain stimulation on a chronic basis. It is proposed to administer a narcotic antagonist to these patients and assess the effect upon the pain relief which they consistently report with stimulation. This study should clearly demonstrate if the effects of electrical stimulation are mediated through the opiate receptor system and should be very important in determining directions of research for the study of stimulation induced analgesia.